There is conventionally known an image processing apparatus that performs a so-called color determination for determining whether a manuscript is a color manuscript or monochrome manuscript. For example, this apparatus determines an expression color expressing an image on a manuscript to determine whether a manuscript type is a color manuscript or a black-and-white manuscript based on image data of the manuscript read by an image reading means such as a CIS (Contact Image Sensor). The color manuscript means that the manuscript is expressed in color and refers to, e.g., a manuscript in which the ratio of a chromatic color area relative to the entire image is higher than or equal to a predetermined threshold. The monochrome manuscript means that the manuscript is expressed in monochrome and refers to, e.g., a manuscript, such as black-and-white manuscript or grayscale manuscript, in which the ratio of the chromatic color area relative to the entire image is lower than a predetermined threshold and the ratio of an achromatic color area relative to the entire image is higher than or equal to a predetermined threshold.